Silicon-Based Light Sources for Silicon Integrated Circuits

Silicon the material per excellence for electronics is not used for sourcing light due to the lack of efficient light emitters and lasers. In this review, after having introduced the basics on lasing, I will discuss the physical reasons why silicon is not a laser material and the approaches to make it lasing. I will start with bulk silicon, then I will discuss silicon nanocrystals and Er3+ coupled silicon nanocrystals where significant advances have been done in the past and can be expected in the near future. I will conclude with an optimistic note on silicon lasing

Routes toward silicon-based lasers

Silicon, the material par excellence for electronics, is not used for light sources because of the lack of efficient light emitters and lasers. In this review, I will discuss the physical reasons why silicon is not a laser material and some approaches to make it lasing. I will start with bulk silicon, then I will discuss silicon nanocrystals and Er 3+ -coupled silicon nanocrystals, where significant advances have been made in the past and can be expected in the near future. I will conclude with an optimistic note on silicon lasing

Monolithic whispering-gallery mode resonators with vertically coupled integrated bus waveguides

We report on the realization and optical characterization of a CMOS-compatible silicon-based microresonator/waveguide coupled system, fully integrated on a silicon chip. The device uses a vertical coupling scheme between the resonator and a buried strip waveguide. We demonstrate that its high optical quality follows from the accurate planarization of the waveguide topography. More importantly, we demonstrate a wafer-scale mass fabrication of freestanding planar resonators suspended in air and coupled to the integrated bus waveguides. A nanometer control of the coupling distances allows for a precise and selective excitation of different mode families of the resonator. This opens the door for the realization of stable all-integrated complex resonator systems for optomechanical and metrological applications, with the potential to substitute the nowadays intensive use of complicated fiber-taper coupling schemes.Comment: 3 pages, 3 figure

Opposite effects of NO2_2 on electrical injection in porous silicon gas sensors

The electrical conductance of porous silicon fabricated with heavily doped p-type silicon is very sensitive to NO$_2$. A concentration of 10 ppb can be detected by monitoring the current injection at fixed voltage. However, we show that the sign of the injection variations depends on the porous layer thickness. If the thickness is sufficiently low -- of the order of few \micro\meter{} -- the injection decreases instead of increasing. We discuss the effect in terms of an already proposed twofold action of NO$_2$, according to which the free carrier density increases, and simultaneously the energy bands are bent at the porous silicon surface.Comment: 3 pages, 3 figures, requires SIunits packag

Reservoir Computing Model For Multi-Electrode Electrophysiological Data Analysis

In this paper we present a computational model which decodes the spatio-temporal data from electro-physiological measurements of neuronal networks and reconstructs the network structure on a macroscopic domain, representing the connectivity between neuronal units. The model is based on reservoir computing network (RCN) approach, where experimental data is used as training and validation data. Consequently, the model can be used to study the functionality of different neuronal cultures and simulate the network response to external stimuli

Photon energy lifter

We propose a time-dependent photonic structure, in which the carrier frequency of an optical pulse is shifted without changing its shape. The efficiency of the device takes advantage of slow group velocities of light attainable in periodic photonic structures. The frequency shifting effect is quantitatively studied by means of Finite Difference Time Domain simulations for realistic systems with optical parameters of conventional silicon technology.Comment: 4 pages 5 figure

Near-ideal spontaneous photon sources in silicon quantum photonics

While integrated photonics is a robust platform for quantum information processing, architectures for photonic quantum computing place stringent demands on high quality information carriers. Sources of single photons that are highly indistinguishable and pure, that are either near-deterministic or heralded with high efficiency, and that are suitable for mass-manufacture, have been elusive. Here, we demonstrate on-chip photon sources that simultaneously meet each of these requirements. Our photon sources are fabricated in silicon using mature processes, and exploit a novel dual-mode pump-delayed excitation scheme to engineer the emission of spectrally pure photon pairs through intermodal spontaneous four-wave mixing in low-loss spiralled multi-mode waveguides. We simultaneously measure a spectral purity of $0.9904 \pm 0.0006$, a mutual indistinguishably of $0.987 \pm 0.002$, and $>90\%$ intrinsic heralding efficiency. We measure on-chip quantum interference with a visibility of $0.96 \pm 0.02$ between heralded photons from different sources. These results represent a decisive step for scaling quantum information processing in integrated photonics

SWIM: A computational tool to unveiling crucial nodes in complex biological networks

SWItchMiner (SWIM) is a wizard-like software implementation of a procedure, previously described, able to extract information contained in complex networks. Specifically, SWIM allows unearthing the existence of a new class of hubs, called "fight-club hubs", characterized by a marked negative correlation with their first nearest neighbors. Among them, a special subset of genes, called "switch genes", appears to be characterized by an unusual pattern of intra- and inter-module connections that confers them a crucial topological role, interestingly mirrored by the evidence of their clinic-biological relevance. Here, we applied SWIM to a large panel of cancer datasets from The Cancer Genome Atlas, in order to highlight switch genes that could be critically associated with the drastic changes in the physiological state of cells or tissues induced by the cancer development. We discovered that switch genes are found in all cancers we studied and they encompass protein coding genes and non-coding RNAs, recovering many known key cancer players but also many new potential biomarkers not yet characterized in cancer context. Furthermore, SWIM is amenable to detect switch genes in different organisms and cell conditions, with the potential to uncover important players in biologically relevant scenarios, including but not limited to human cancer

Interferometric cavity ring-down technique for ultra-high Q-factor microresonators

Microresonators (MRs) are key components in integrated optics. As a result, the estimation of their energy storage capacity as measured by the quality factor (Q) is crucial. However, in MR with high/ultra-high Q, the surface-wall roughness dominates the intrinsic Q and generates a coupling between counter-propagating modes. This splits the usual sharp single resonance and makes difficult the use of classical methods to assess Q. Here, we theoretically show that an interferometric excitation can be exploited in a Cavity Ring-Down (CRD) method to measure the ultimate Q of a MR. In fact, under suitable conditions, the resonant doublet merges into a single Lorentzian and the time dynamics of the MR assumes the usual behavior of a single-mode resonator unaffected by backscattering. This allows obtaining a typical exponential decay in the charging and discharging time of the MR, and thus, estimating its ultimate Q by measuring the photon lifetime.Comment: 5 pages and 2 figure

Band gap characterization and slow light effects in one dimensional photonic crystals based on silicon slot-waveguides.

We investigate the photonic properties of one dimensional photonic crystals realized on Silicon On Insulator channel slot-waveguide to engineer slow light effects. Various geometries of the photonic pattern have been characterized and their photonic band-gap structure analyzed. The optimal geometry has been further used to realize a coupled resonator optical waveguide (CROW). A first optimization of these CROW devices shows a group velocity of more than c/10 at 1.55 mum. Full three dimensional calculations based on the planar wave expansion method have been used to compute the band diagram while full three dimensional calculations based on finite difference time domain methods have been used to study light propagation